Respiratory chains bacterial

Not all the cellular DNA is in the nucleus some is found in the mitochondria. In addition, mitochondria contain RNA as well as several enzymes used for protein synthesis. Interestingly, mitochond-rial RNA and DNA bear a closer resemblance to the nucleic acid of bacterial cells than they do to animal cells. For example, the rather small DNA molecule of the mitochondrion is circular and does not form nucleosomes. Its information is contained in approximately 16,500 nucleotides that func-tion in the synthesis of two ribosomal and 22 transfer RNAs (tRNAs). In addition, mitochondrial DNA codes for the synthesis of 13 proteins, all components of the respiratory chain and the oxidative phosphorylation system. Still, mitochondrial DNA does not contain sufficient information for the synthesis of all mitochondrial proteins most are coded by nuclear genes. Most mitochondrial proteins are synthesized in the cytosol from nuclear-derived messenger RNAs (mRNAs) and then transported into the mito-chondria, where they contribute to both the structural and the functional elements of this organelle. Because mitochondria are inherited cytoplasmically, an individual does not necessarily receive mitochondrial nucleic acid equally from each parent. In fact, mito-chondria are inherited maternally. 

Fullerene showed antibacterial activity, which can be attributed to different interactions of C60 with biomolecules (Da Ros et al., 1996). In fact, there is a possibility to induce cell membrane disruption. The fullerene sphere seems not really adaptable to planar cellular surface, but for sure the hydrophobic surface can easily interact with membrane lipids and intercalate into them. However, it has been demonstrated that fullerene derivatives can inhibit bacterial growth by unpairing the respiratory chain. There is, first, a decrease of oxygen uptake at low fullerene derivative concentration, and then an increase of oxygen uptake, which is followed by an enhancement of hydrogen peroxide production. The higher concentration of C60 seems to produce an electron leak from the bacterial respiratory chain (Mashino et al., 2003). 

Complex IV Cytochrome c to 02 In the final step of the respiratory chain, Complex IV, also called cytochrome oxidase, carries electrons from cytochrome c to molecular oxygen, reducing it to H20. Complex IV is a large enzyme (13 subunits Mr 204,000) of the inner mitochondrial membrane. Bacteria contain a form that is much simpler, with only three or four subunits, but still capable of catalyzing both electron transfer and proton pumping. Comparison of the mitochondrial and bacterial complexes suggests that three subunits are critical to the function (Fig. 19-13). 

FIGURE 19-33 Bacterial respiratory chain, (a) Shown here are the respiratory carriers of the inner membrane of E. coli. Eubacteria contain a minimal form of Complex I, containing all the prosthetic groups normally associated with the mitochondrial complex but only 14 polypeptides. This plasma membrane complex transfers electrons from NADH to ubiquinone or to (b) menaquinone, the bacterial equivalent of ubiquinone, while pumping protons outward and creating an electrochemical potential that drives ATP synthesis. 

This hypothesis presumes that early free-living prokaryotes had the enzymatic machinery for oxidative phosphorylation and predicts that their modern prokaryotic descendants must have respiratory chains closely similar to those of modern eukaryotes. They do. Aerobic bacteria carry out NAD-linked electron transfer from substrates to 02, coupled to the phosphorylation of cytosolic ADP. The dehydrogenases are located in the bacterial cytosol and the respiratory chain in the plasma membrane. The electron carriers are similar to some mitochondrial electron carriers (Fig. 19-33). They translocate protons outward across the plasma membrane as electrons are transferred to 02. Bacteria such as Escherichia coli have F0Fi complexes in their plasma membranes the F portion protrudes into the cytosol and catalyzes ATP synthesis from ADP and P, as protons flow back into the cell through the proton channel of F0. 

Not all proton pumps are driven by electron transport. ATP synthase is reversible, and if Ap is low, hydrolysis of ATP can pump protons out of mitochondria or across bacterial plasma membranes.268 Cells of Streptococcus faecalb, which have no respiratory chain... 

Cytochrome c4 s are believed to constitute parts of bacterial respiratory chains. In the present context, the following properties specific to P. stutzeri cyt c4 are important [8, 40] ... 

Electron transfer Basic to the function of the respiratory chains of mitochondria and bacterial pathogens. 

Figure 2 The chemiosmotic theory of respiration. The mitochondrial or bacterial membrane (yellow) provides resistance to proton conduction. The respiratory chain generates a proton electrochemical gradient across the membrane by redox-coupled proton translocation (Figure 1). This gradient is used as the driving force for synthesis of ATP, as catalyzed by the H+-ATP synthase in the same membrane...

In bacterial chromatophores the RC and the b/c, complex are arranged to form a cyclic electron transfer system possibly mediated by the diffusion of ubiquinone and cyt. Cj these carriers are, however, also coupled to other multienzyme complexes forming the respiratory chain and perform the aerobic metabolism of these facultative photosynthetic organisms [254]. The electrogenic steps of the photosynthetic cycle take place both within the RC and the 6/cj complexes and can be monitored by the electrochromic spectral shift of endogenous carotenoids and on the basis of their response to specific inhibitors and kinetics. When induced by a short laser flash the carotenoid signal displays three distinct kinetic phases (r,/2 10 h/i 5 jas... 

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